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Unformatted text preview: 5/9/2004 H133 Spring 2004 1 Chapter T1 • Introduction to Statistical Mechanics This topic does not have the “strangeness” that quantum mechanics had…but it does have some very interesting aspects. Statistical Mechanics describes the behavior of macroscopic objects Newtonian Mechanics: o o o EM were dealing with the fields setup by charged objects both stationary and moving. Quantum: o Definitely dealing with microscopic objects and treating them as point-like. Consider gas molecules in a balloon. How do we understand the pressure on the balloon walls? o • This is where statistical mechanics saves us. We can determine the macroscopic properties without worrying about the individual objects in the problem. o Works when ! We need to define a new set of variables that are useful for systems of many particles Temperature, Pressure, Volume, N states , Entropy, etc Note: It makes little sense to define these for a single object…these are truly properties of the “full system”. 5/9/2004 H133 Spring 2004 2 Irreversible Processes • The fundamental idea that this unit is structured around is the concept that certain processes are not reversibe. The common example is to think about making a movie of some physical process, then think about watching the moving in reverse. Certain actions, if you saw them in reverse, would not strike you as strange. Two fundamental particles colliding (billiard balls) An electron absorbing a photon and making a transition to a higher energy level. A ball being thrown in the air and then caught. One of the reasons that these would not strike you as strange is that these involve reversible processes. Basic Newtonian Mechanics and Quantum Mechanics are time symmetric These theories don’t have a “forward arrow” in time. Exception: QM, CP Violation…intense interest now. Forward Reverse Forward Reverse 5/9/2004 H133 Spring 2004 3 Irreversible Process • There are many processes that would strike you as being very strange if the movie was played in reverse: A rock being throw into a pond: A block sliding on the table with friction bringing it to a stop....
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